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Electrochemical system centered on hierarchically carbon-based metal sulphide assemblies are of great fame for competent supercapacitors. Herein, the synthesis of a hierarchical CNT anchored MoS2–Bi2S3 nanocomposite is reported. Attractively, a vertically grown Bi2S3 nanorods supported on MoS2 nanosheets with carbon framework acts as a highly effective electrode in alkaline electrolyte. More interestingly, this hierarchical structure and synergetic upshot of CNT and composites provide excess coverage of active sites with improved conductivity and stability. Advancing from the physical and compositional properties of nanocomposites, the specific capacitance of MoS2–Bi2S3@CNT composites is measured to be 1338 F/g at 10 mV/s, columbic efficiency of 99.5% over 10000 cycles and long-term stability (60% retention at 0.5 A g−1 over 2000 cycles and 34.6% up to 10000 cycles). The success of this MoS2–Bi2S3@CNT composite may be attributed to the structural advantages, admirable cyclic stability, and better capacitance retention for supercapacitor applications.

Amorphous tungsten (VI) trioxide thin films were deposited on rigid Ni-foam and flexible PET substrates using RF magnetron sputtering technique. The impacts of sputtering RF power on microstructure, morphology, compositional and electrochemical properties of the deposited thin films were investigated by using Raman, FE-SEM, XPS and electrochemical techniques. The thicknesses of the deposited films were increased from 70 to 105 μm as a function of RF power. The films contain uniform nanoparticles and the observed sizes are in the range of 25–70 nm. The films of WO3@Ni and WO3@PET deposited at an optimum RF power of 100 W exhibited the high areal capacitance of 22.01 mF/cm2 and 9.76 mF/cm2 with good cyclic retention of 81.03% and 69.53% after 5000 cycles respectively. Further, two solid-state symmetric supercapacitor (SSC) devices were assembled which shows pseudocapacitive behaviour. The devices delivered moderate energy densities of 0.48 μWh/cm2 and 0.20 μWh/cm2 and power densities of 312 μW/cm2 and 150 μW/cm2 for rigid Ni foam and flexible PET based devices respectively. This result demonstrated that the binder free in-situ deposition of WO3 films deposited at an optimum RF power of 100 W is more suitable to fabricate supercapacitor devices.

With the increase in the importance of using green energy sources to meet the world's energy demands, attempts have been made to push perovskite solar cell technology toward industrialization all around the world. Improving the properties of perovskite materials as the heart of PSCs is one of the methods to fabricate favorable photovoltaic (PV) solar cells based on perovskites. Here, cadmium chloride (CdCl

Owing to its good redox properties, excellent electron–hole pair generation, wide band gap and outstanding chemical stability, SnO2 has been considered as a promising bifunctional material for supercapacitors as well as photocatalysts, but its poor conductivity and low surface area limit the specific capacitance and catalytic efficiency. To enhance the functional properties of SnO2, herein, lanthanum doped tin oxide anchored with reduced graphene oxide (La–SnO2@rGO) heterostructures has been first employed. The properties of the synthesized materials were characterized by using various analytical tools. The maximum specific capacitance of 321 F g−1 at a current density of 1 A g−1 was obtained for the La–SnO2@rGO electrode. The fabricated asymmetric supercapacitor using the La–SnO2@rGO//activated carbon device exhibited high energy and power density of 41.2 W h kg−1 and 750 W kg−1 at a current density 1 A g−1, respectively. Also, the device notably retained 82% specific capacitance after 10 000 charge–discharge cycles. On the other hand, the La–SnO2@rGO heterostructure was utilized for the photocatalytic degradation of the methylene blue dye under visible light irradiation which showed a maximum degradation efficiency of 98%. This study contributes to the development of a facile strategy for the preparation of heterostructured materials suitable for the bifunctional applications of high capacitive supercapacitor electrodes and visible light dye degradation.

In this article, Nickel doped rutile structure tin oxide (SnO₂) nanoparticles have been prepared by simple chemical co-precipitation method and prepared samples were characterized by Powder X-ray Diffraction, Fourier transform infrared Spectroscopy, Microraman analysis, Photoluminescene Spectroscopy, UV-Visible Spectroscopy, Energy dispersive analysis and Field emission scanning electron microscope. XRD studies revealed the single phase tetragonal rutile structure with space group of P42/mnm. The average crystallite size of the particles was decreased from 27 to 22 nm with increasing Ni doping concentration. FTIR spectra confirmed the presence of various bands such as O-H, C-H, Sn-O-Sn. Raman modes Eg, A1g and B2g were assigned at 478, 630 and 740 cm-1 which confirmed the single phase of pure and Ni doped SnO₂ nanoparticles. The photoluminescence spectra confirmed that the defect related emissions increased with increasing of Ni concentration. The UV absorption spectra showed that the absorption of the particles decreased with increasing Ni concentration and the band gap values decreased from 3.7 to 3.4 eV. EDX spectra confirmed the presence of Sn, Ni, O in pure and doped samples. The photocatalytic activity of the pure and Ni doped SnO₂ nanoparticles were analyzed by using methylene blue dye under visible light irradiation. It is concluded Ni (7%) doped SnO₂ nanoparticles have higher degradation efficiency compared to pure SnO₂ nanoparticles.

Pure and rare earth elements of samarium (Sm), lanthanum (La) and neodymium (Nd) doped cadmium oxide (CdO) thin films were deposited on glass substrates by radiofrequency magnetron sputtering at room temperature. The influence of rare earth dopants on the microstructural, morphological and optoelectronic properties of the CdO thin films were studied elaborately. The X-ray diffraction studies revealed the polycrystalline with face centered cubic structure of CdO thin films. The structural defects were increased with increase of dopant’s ionic radii. The presence of the dopants in host CdO thin films was confirmed by X-ray photoelectron spectroscopic analysis. The roughness of the films was decreased for the doped samples and Nd doped CdO thin film has the minimum roughness value of 1.29 nm. All the films exhibited high transmittance in visible range and well pronounced Moss-Burstein shift was observed in the band gap value. Emission bands of photoluminescence spectra depicted the presence of oxygen vacancies. Hall Effect measurement showed an increase in carrier concentration and electrical conductivity of the films with the addition of dopants. The suitable combination of high conductivity (2872 Ω−1·cm−1) with optical transparency (88%) and lower surface roughness of Nd doped CdO thin film, makes it a potential candidate for the transparent conducting oxide in optoelectronic devices.

The peculiar morphology of nanorods mixed with microspheres of manganese carbonate (MnCO3) doping with different percentages (0, 2, 4, 6%) of silver (Ag) was synthesized by simple co-precipitation method. The effect of Ag doping on structural, morphological and compositional properties of MnCO3 were investigated. XRD results revealed that the synthesized samples have hexagonal-rhombohedral structure and the peaks are shifted towards higher angles with increasing Ag content. The pure MnCO3 exhibited microsphere like morphology with the size in the rage of 0.8–2.5 μm. XPS analysis confirmed the presence of Mn, C, O and Ag elements. The specific capacitance values are calculated and 4% Ag-doped MnCO3 electrode exhibited a high specific capacitance of 554.6 Fg-1 at a current density of 0.5 Ag-1, good rate capability of 54.74% and excellent cycle stability of 87.22% capacitance retention after 1000 cycles. From these results, Ag-doped MnCO3 could be preferred as the potential competitor for future electrochemical supercapacitor devices.

The different attractive morphologies of micro-nano assembled sphere, pseudo sphere, rock candy and cube-like Mn2O3/NiO composites were synthesised by the facile solvothermal method through varying the solvents and their volume ratio. The structural, morphological and compositional properties of synthesised samples were investigated by using powder X-ray diffraction (XRD), FE-SEM, EDS and XPS. The TG/DTA results confirmed the transformation of MnCO3/NiCO3 to Mn2O3/NiO structures. XRD results revealed that the synthesised samples exhibited the body-centred cubic of Mn2O3 and face-centred cubic of NiO. FESEM images depicted the formation of different micro-nano assembled morphologies. XPS study confirmed the presence of manganese, nickel and oxygen elements and their oxidation states. Pseudocapacitance properties of Mn2O3/NiO electrodes were evaluated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy using 1M KOH electrolyte solution. The specific capacitance values of all the synthesised samples were calculated and the morphology of rock candy like Mn2O3/NiO composite exhibited superior properties of high specific capacitance of 566.21 Fg−1 at a current density of 0.5 Ag−1, better rate capability of 63.25% and good cycling stability of 87.42% capacitance retention even after 1000 cycles. From these results, the well morphological ordered Mn2O3/NiO composites may be preferred as the future electrode materials for electrochemical supercapacitor energy storage devices.

In this work, we have synthesized Mn-doped SnO2@ZnO nanocomposite for photo degradation of Methylene blue and Rhodamine B dyes upon visible light irradiation. The crystal structure, functional group, optical absorption, defect related emission, morphology, purity and binding energy state of synthesized samples were identified by using various analytical tools. The crystal structure revealed the rutile tetragonal, hexagonal wurtzite for SnO2 and ZnO samples and the average crystal sizes were found in the range of 23.3 nm to 16.7 nm for the synthesized samples. The optical absorption peaks were shifted to higher wavelength side and optical band gap values were found between 3.52 eV and 2.77 eV which confirm the formation of hetero-junction of SnO2@ZnO composites. The field emission scanning electron spectroscopy (FESEM) revealed the spherical grain morphology for pure and composite samples. The energy dispersive spectra (EDS) and element mapping confirms the purity of the synthesized samples. The X-ray photoelectron spectroscopy (XPS) revealed that the composition and energy state of Mn4+, Sn4+ and Zn2+ for composite samples. The photocatalytic degradation results clearly indicate that the Mn-doped SnO2@ZnO nanocomposite has higher degradation efficiency of 98% and 92% for the Methylene blue and Rhodamine B dyes, respectively and is higher than the other synthesized samples. The present study reveals a low cost and highly efficient photo-catalyst which works up on visible light irradiation for the purification of waste water from industries.

Pure and cobalt (Co)-doped tin oxide (SnO2) nanoparticles were prepared by using a simple co-precipitation method, and the effect of doping on structural, morphological and optical properties was studied. X-ray diffraction revealed a cassiterite tetragonal SnO2 structure with the space group of P42/mnm and without crystalline phases for the samples-doped with higher concentrations. The average crystalline size was found to be between 26.4 nm and 23.1 nm. Fourier-transform infrared spectra depicted the presence of O–H, C–H and Sn–OH absorption bands. It was observed from ultraviolet–visible spectra that the optical band gap values were decreased from 3.69 eV for pure SnO2 to 3.47 eV for 7% Co-doped SnO2. The photolumenescene emission spectra showed that the defect- and emissions-related peaks and the intensity of the peaks decreased with increasing Co concentrations. The presence of tin, oxygen and Co species were found from energy dispersive x-ray spectra. The photocatalytic activities of pure and Co-doped SnO2 nanoparticles were investigated by studying the photodecomposition of brilliant green dye, an organic pollutant. The 7% Co-doped SnO2 had higher photocatalytic activity compared to the pure SnO2, and a maximum degradation efficiency of 91% has been obtained under visible light irradiation.

Pure and alkaline earth metal (Ba2+, Ca2+ and Mg2+)-doped tin oxide nanoparticles were synthesized by simple co-precipitation, and their structural, optical, functional, morphological and compositional properties were analyzed in detail using powder X-ray diffraction, UV–visible spectroscopy, photoluminescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy and energy-dispersive analysis of X-ray (EDAX). XRD revealed the formation of rutile tetragonal structure, and the crystallite size has decreased from 28 to 24 nm by the addition of alkaline metal dopants. FTIR spectra confirmed the presence of fundamental vibration modes of SnO2. The optical band gap energy was decreased to 3.05, 3.19 and 2.98 eV by introducing Ba2+, Ca2+ and Mg2+ ions, respectively. Photoluminescence spectra showed defect-related emission peaks, and their intensities were found to increase in doped SnO2 samples. EDAX spectra confirmed the presence of Sn, O, Ba, Ca and Mg elements. The photocatalytic activity of pure and alkaline metal-doped SnO2 catalyst has been investigated under visible light irradiation by using methylene blue dye. The results showed that the Mg-doped SnO2 catalyst has a higher photodegradation efficiency (~ 95.7%) compared with other investigated samples.

Highly transparent and conducting samarium doped cadmium oxide (CdO: Sm) thin films were deposited on glass substrates at room temperature by radio frequency (RF) magnetron sputtering technique using CdO(90 wt%): Sm2O3(10 wt%) mixed alloy target in pure argon atmosphere. The influences of RF power and Sm incorporation on structural, morphological, optical and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the deposited films are polycrystalline nature and RF power has a large impact on the preferred orientation of the films. The X-ray photoelectron spectroscopy studies confirmed the presence of divalent cadmium (Cd2+) and trivalent samarium (Sm3+) in the deposited film. It is found from the atomic force microscopic analysis that the films were highly smooth with low roughness value of about1.3 nm. High transmittance value greater than 80% was retained by the films in visible and near infrared regions and the band gap value decreased with the increase of RF power by quantum confinement. At the moderate RF power of 200 W, the film has low resistivity of the order of 1.283 × 10−4 Ω cm, high mobility 157.8 cm2/V and a high figure of merit 769.04 (Ω cm2)−1 which could be used as an alternative TCO layer for future optoelectronic devices.

Transparent and conducting cadmium oxide (CdO) thin films were deposited on glass substrates at room temperature using radio frequency (RF) magnetron sputtering method. The carrier concentration and electron mobility are the key factors for the conducting properties of CdO thin films. The grain size, crystallinity, thickness, surface roughness and band gap of CdO thin films play an important role in optical and electrical properties. In this study, dual behaviour of CdO thin films is studied as a function of RF sputtering power. Crystalline quality, micro structure, surface morphology and optical and electrical properties of sputtered CdO thin films were investigated. The structural analysis revealed that the deposited CdO films were polycrystalline in nature with cubic structure ( Fm 3 ¯ m space group). The grain sizes were found to be increased with increase of RF power from 100 to 150 W and then decreased at high power (200 W). The optical studies revealed that all the films exhibited higher transmittance in visible and near infrared region and the optical energy band gap value decreased from 2.62 to 2.46 eV with increase of RF power. Luminescence spectra exhibited two strong emission peaks at 484 and 519 nm. The resistivity of CdO thin films gradually decreased with an increase of sputtering power and reached a minimum value of 3.041 × 10−4 Ω cm at 200 W. A maximum mobility of 67.01 cm2/Vs was found for the sample prepared at the sputtering power of 150 W.

Single phase cadmium stannate thin films were deposited on glass substrates through rf magnetron sputtering by varying rf power and keeping substrates at room temperature. The effect of rf power on physical properties of the films and the correlations were systematically investigated. It has been found from XRD that structural phase transition occurred from amorphous to spinel structure with increase of rf power. AFM images revealed that the deposited films show smooth surface with nano grains. High transmittance was retained by the films in visible region and the band gap was decreased from 3.05 to 2.49 eV for increasing rf power by quantum confinement effect. The Mott-Davis model and drude model were used to evaluate the optical constants and free carrier absorption. The electrical resistivity of the films varied in three orders of magnitude as a function of rf power which could be explained by oxygen vacancies formation. From these results, the films deposited at 150 W has the low resistivity of the order of 10 −3 Ω cm with high optical transparency as 80% which could be the preferred conditions to deposit high quality films for future TCO layers for cadmium based CdTe/CdS solar cell devices.

Cerium (Ce) doped SnO2/g-C3N4 composites were synthesized by a facile hydrothermal method. The obtained Ce doped SnO2/g-C3N4 composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), scanning electron microscope (SEM), energy dispersive spectra (EDS), elemental mapping and X-ray photoelectron spectroscopy (XPS). An electrode made of Ce doped SnO2/g-C3N4 exhibited a maximum specific capacitance of 274 F/g at 1 A/g current density. The supercapacitor device fabricated by using Ce-SnO2/g-C3N4//Activated Carbon as electrodes has showed an energy and power densities of 39.3 W h kg−1 and 7425 W kg−1. The asymmetric device gives the retention of 84.2% after completing 5000 cycles. When the same, Ce-SnO2/g-C3N4, composite is used as a photo-catalyst for reduction of methylene blue dye under visible light irradiation, exhibits a higher degradation efficiency of 98% which is higher efficiency compared to all other synthesized samples.

In this work, we report enhanced specific capactance and cycle stability of Fe-SnO2@CeO2 electrode for supercapacitor applications. The Fe-SnO2@CeO2 nanocomposite was synthesized through a simple chemical co-precipitation method. The electrochemical performances of the Fe-SnO2@CeO2 nanocomposite electrode are assessed by using cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy techniques. In three electrode system, the Fe-SnO2@CeO2 nanocomposite electrode is exhibited a maximum specific capacitance of 348 F/g at a current density of 1 A/g. Further, the asymmetric supercapacitor (ASC) device performance has been evaluated and the ASC device produces a specific energy and specific power of 32.2 W h kg−1 and 747 W kg−1 at a current density of 1A/g, respectively. The device exhibited the capacitance retention of 85.05 % over 5000 cycles of operation. This study confirms that the Fe-SnO2@CeO2 is an alternative electrode material for high energy storage supercapacitor applications.

In this article, we synthesize the bifunctional materials of various transition metals (TM) (Co, Ni and Mn) doped SnO2@MoS2 composites for enhanced energy storage and improved photocatalytic activity for removing organic pollutants. Herein, we use a facile hydrothermal method for sample synthesis and the physico chemical properties of the synthesized samples were investigated in detail using various analytical tools. The energy dispersive X-ray spectra and elemental mapping confirmed the presence of species in the synthesized samples. X-ray photoelectron spectroscopy analysis revealed the corresponding energy state of various TM doped SnO2@MoS2 samples. The Mn doped SnO2@MoS2 composite exhibited a higher specific capacitance of 242 F/g at a current density 0.5 A/g. The capacitance retention of 83.95% was observed after 5000 continuous charge/discharge cycles. Further, the Mn doped SnO2@MoS2 composite had higher degradation efficiency (97%) compared to all other samples using methylene blue as an organic dye under visible light irradiation. Henceforth, this study demonstrates the optimum concentration of Mn doped SnO2@MoS2 composite is the outstanding bifunctional materials for supercapacitor and photocatalytic applications.

Synthesis of high energy density and long durability electrode materials are huge urgency for futuristic hybrid supercapacitors (HSCs). In the present work, self-assembled three-dimensional (3D)-mesoporous regimented pristine and neodymium (Nd) doped α-Mn2O3 microspheres (MSs) are prepared by simple hydrothermal method. Due to uniform morphology, presence of oxygen vacancies, mesoporous robust structure, and optimum doping (Nd5%-doped Mn2O3 3D-MSs) offers a high specific capacitance of 862.14 F g−1 (431.07 C g−1) at 0.5 A g−1 with superior cycling retention of 97.30% after 2000 cycles. Additionally, a pouch-type HSC device is fabricated using Nd5%-Mn2O3 3D-MSs as a battery-type positive electrode and activated carbon (AC) as a capacitive-type negative electrode. The fabricated device delivers a maximum energy density of 32.26 Wh kg−1 at a power density of 800 W kg−1 with superior cyclic retention and exhibit a little loss of 4.56% after 10,000 cycles. This superior performance is due to robust microstructures that can alleviate swelling and shrinking of active material at cycling test. Two pouch-type HSCs are connected in series to power light-emitting diodes (LEDs) for real-time applicability. Overall, this study demonstrates that rational doping, porous architecture, oxygen vacancies, and robust micro-nano structure greatly assist to achieve high energy density as well as long life HSCs devices.

A simple co-precipitation method has been used to synthesis SnO2 and different transition metal (Fe, Cu and Zn) doped SnO2 spherical nanostructures. The influence of doping concentration on the structural, optical, functional and morphological properties were carefully analysed by using X-ray diffraction, Fourier Transform Infrared Spectroscopy, UV–Visible spectroscopy and Scanning Electron Microscopy studies. The XRD pattern declared the formation of cassiterite rutile SnO2 with tetragonal structure. No impurity peaks correspond to the transition metal dopant was observed in the doped SnO2 samples. The average crystallite size was found to be 27.2, 24.1, 22.3 and 21.8 nm for pure and Fe, Cu and Zn-doped samples, respectively. The EDX spectra and element mapping assessed the presence of Sn, O, Fe, Cu and Zn species. The SEM images showed the spherical morphology for the synthesized pure and TM-doped samples. X-ray photoelectron spectra confirmed the electronic state and binding energy of the Sn, Cu, Zn, Fe and O. The electrochemical performance of the prepared electrodes were evaluated by galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The nanostructured Fe doped SnO2 electrode revealed a favorable specific capacitance of 270 F/g at a current density of 0.5 A/g and also it has excellent cycling stability of 98% retention over 2000 charging discharging cycles.

Transparent and conducting thin films of pure and gadolinium(Gd) doped cadmium oxide (CdO) were deposited on glass substrates by RF magnetron sputtering at ambient temperature to develop indium free, alternate transparent conducting electrode for optoelectronic devices. The impacts of Gd doping and film thickness on physical properties of the deposited films were investigated. Mechanism of transmittance, conduction and the scattering process were also discussed. The films showed cubic structure with predominant orientation along (111) plane. All the deposited films were smooth and homogeneous with decreasing roughness from 2.23 nm to 1.69 nm for Gd doped CdO thin film. Pristine CdO film showed peculiar morphology of nano pyramidal shaped grains on the surface. The average transmittance of the films increased from 79% to 88% with the doping of Gd. The Gd doped CdO (GCO) film at a thickness of 900 nm exhibits a maximum transmittance of 93% in visible range. The Gd doped CdO film deposited at a thickness of 900 nm showed the best optoelectronic properties with high average transmittance (88%) and low resistivity (7.203 × 10−5 Ω cm). This result indicates that the Gd doped CdO thin films deposited with suitable thickness can be used as an alternative for high performance TCO in various optoelectronic devices.

In this paper, the structural and magnetic behavior of Ni/Mn co-doped ZnO nanoparticles (NPs) synthesized by co-precipitation method are presented. Powder X-ray diffraction data confirm the formation of a single phase wurtzite type of ZnO structure for all the synthesized Ni, Mn doped and co-doped ZnO nanoparticles. The average crystallite size of NPs is found to be 26–38 nm. FTIR and UV spectroscopic results confirm the incorporation of the dopant into the ZnO lattice structure. Photoluminescence intensity varies with doping due to the increase of oxygen vacancies. Furthermore, M-H curve demonstrates that the Ni/Mn co-doped ZnO NPs possess obvious ferromagnetic characteristics at room temperature. Our study enhances the understanding of the novel performances of transition metal co-doped ZnO NPs and also provides possibilities to fabricate spintronic devices.

Recent advances in the development of manganese carbonate (MnCO3) have opened up new attractive electrode material for supercapacitor applications. However, limited internal specific capacitance and long cycle stability of MnCO3 due to its low electrical conductivity, poor interfacial properties and simple geometric configurations need to be further improved. Development of smart micro-nano architecture for electrode materials preparation is a critical challenge nevertheless it provides high specific capacitance, rich rate capability and long cycle stability. To achieve this, the facile strategy has been adopted to synthesis self-assembled micro-nano architecture of MnCO3 via simple co-precipitation, microwave and hydrothermal-assisted methods. The proposed first principle calculation study confirmed the weak interaction behaviour between OH− and MnCO3 and tiny volume expansion of unit cell are favourable for rapid charging mechanism and high rate performance. The optimised complex grain growth of 3D MS/NCs MnCO3 electrode delivered an ultrahigh specific capacitance of 302.47 F g−1, high rate capability and long cycle stability. Moreover, an asymmetric supercapacitor is employed in as-prepared 3D MS/NCs MnCO3 as positive electrode and activated carbon as negative electrode which exhibits high specific energy of 18.07 W h kg−1, power density of 7498 W kg−1 and superior capacitance retention of 98.79% even after 10,000 cycles. From these results, we concluded that the self-assembled micro-nano structures are preferred as the future promising electrode architecture for supercapacitors.

In this paper, we present the structural, morphological, optical and magnetic properties of Zn1−x A x O (A = Ni, Co and x = 0.20 mol%) and Zn0.80Ni0.10Co0.10O nanoparticles synthesized by a chemical co-precipitation method. Powder X-ray diffraction data confirm the formation of a single-phase wurtzite-type ZnO structure for all the samples. FTIR and EDS measurements ensure that the divalent Ni and Co ions are incorporated in the wurtzite host matrix without any impurity phase. Photoluminescence and Raman spectra indicate the presence of donor defects and oxygen vacancies in the prepared samples. In VSM analysis, undoped ZnO nanoparticles exhibit diamagnetic behavior at room temperature. A systematic increase in ferromagnetic moment (~0.70 emu/g) is observed for Ni-, Co-doped and Co co-doped Ni/ZnO at 300 K. The exchange interaction between delocalized carriers and the localized ‘d’ spins of Ni and Co ions is predicted as the cause of the room temperature ferromagnetism.

We report systematic studies of the magnetic properties of Ni and Mn co-doped ZnO nanoparticles prepared by co-precipitation method. Structural characterization reveals that Ni and Mn ions substituted into ZnO lattices without any secondary phases formation. Photoluminescence and Raman spectra shows that the Ni/Mn were doped into the ZnO lattice resulting slight shift in near-band-edge emission. Moreover, the novel Raman peak at 586 cm−1 indicates two kinds of cations via doping that could affect the local polarizability. Magnetic measurements of the nanoparticles exhibits ferromagnetic behavior at room-temperature.

We present a numerical method for the solution of the Falkner-Skan Equation. The method uses a coordinate transformation to convert the physical problem on a semi-infinite physical domain to a problem on a fixed computational domain. Then, after using a suitable change of variables, the third-order boundary value problem is solved using a shooting technique. The numerical solutions obtained by the present method are in agreement with those obtained by previous authors.

A Taylor series technique for obtaining pointwise bounds for the solution of a class of diffusion problems in physiology is presented. Simple analytic bounding functions are obtained using an integral representation for the solution. Computations are performed in interval arithmetic, and thus lower and upper bounds are obtained simultaneously. Higher-order Taylor coefficients are computed using simple recursion relations. The oxygen diffusion problem in spherical cells is presented as an illustrative example. For this example, the present technique is computationally more efficient than the existing ones in that it yields sharper bounds with fewer integration steps.

Stefan problems are described by a parabolic partial-differential equation, along with two boundary conditions on a moving boundary, which is to be determined as part of the solution. The purpose of this paper is to develop a finite-element method for the solution of a one-dimensional Stefan problem. First, a coordinate transformation is used to transform the changing physical domain into a fixed computational domain. Then, the weak or Galerkin formulation of the initial boundary value problem is used to reduce it to a system of initial-value problems in ordinary differential equations. Several finite-difference marching methods are used to solve the resulting initial-value problems. The method is developed and illustrated using the Stefan problem concerning the heat transfer in an ice-water medium. The computational results are in very good agreement with the results produced earlier by several authors.

A numerical method for the solution of an inhomogeneous nonlinear diffusion problem that arises in a variety of applications is presented. The diffusion coefficient in the underlying diffusion process is concentration- as well as distance- dependent. We wish to determine the concentration of the diffusing substance in a semi-infinite domain at any time, starting with a given initial concentration. The method of solution begins by first mapping the semi-infinite physical domain to a finite computational domain. An implicit finite-difference marching procedure is then used to advance the solution in time. Numerical results are presented for several physical problems. We observe that the present numerical solutions are in good agreement with the analytical solutions obtained previously by other researchers.

A numerical method for the solution of two-dimensional Stefan problems will be presented in this paper. The major features of the method are the use of boundary-fitted coordinates, and an implicit marching procedure. Illustrative examples will be given in order to demonstrate the accuracy of the method. Numerical results of the present method will be compared with those obtained previously.

Free-surface flows define an area of a great deal of engineering interest. In this paper, we present a finite-difference method for an accurate and efficient solution of potential flows with a free surface. Boundary-fitted coordinates are used to eliminate the difficulty introduced by the free surface. The method is illustrated with applications to problems involving unsteady two-dimensional flows.

A numerical technique for obtaining pointwise bounds for the solution of a class of nonlinear boundary-value problems in physiology is presented. Simple analytic bounding functions are obtained using an integral representation for the solution. The computations are performed in interval arithmetic, thus obtaining lower and upper bounds simultaneously. The oxygen diffusion problem in spherical cells and a nonlinear heat-conduction model of the human head are presented as illustrative examples. For these examples, the present technique is computationally more efficient than the existing ones in that it yields sharper bounds with fewer integration steps.

Several variable time-step (VTS) methods have been suggested by various authors for the solution of the one-dimensional Stefan problem. All of these methods involve an iterative computation of the time-step for a given advancement of the moving boundary. During each iteration, a linear system of equations needs to be solved. Some modifications of an existing VTS method due to Gupta and Kumar [1] are presented in this paper. The modifications include the use of a tridiagonal solution of the linear system involved instead of Gaussian elimination and the use of an integral relationship to improve the time step instead of a difference formula as in [1]. The first modification yields increased efficiency while the second results in increased accuracy. Numerical results are presented for two problems.